Certain types of bus construction, such as buses which travel relative long distances at highway speeds between stops, desire minimal airflow drag and accordingly require that the air conditioning and air distribution system be confined within the normal outer structure of the bus. Typical prior art approaches to air conditioning and distribution systems for such buses spread the components of the cooling portion of the system about the bus, and the heating system is normally separate from the cooling system.
The distribution of air in a bus for heating, cooling, and fresh air circulation, is a major factor in obtaining satisfactory passenger comfort. The cooling of a bus is best accomplished with air from roof ducts which extend along the outer roof corners. Heating of a bus is best accomplished with air from floor and sidewall ducts.
Cooling a bus with floor and sidewall ducts is not efficient, and requires a relative long pull-down time which is undesirable for commuter buses, for example, which sit all day in the sun waiting for the evening part of the commute.
Heating a bus via overhead ducts is generally unsatisfactory as the bus floor is usually too cold and the ceiling too warm, due to the natural convection of the air.
Thus, it is conventional to heat a bus using floor and sidewall ducts, drawing return air to the heating unit at the floor level. The air at floor level, however, is not the most indicative of passenger compartment air temperature, and even more detrimental, it contains the highest dirt content of any air in the bus.
The noise produced by the motors and blowers of the air conditioning and air circulation system must be controlled for passenger comfort. Introducing a circuitous path between the air conditioning system and the bus ducting reduces noise level. However, this results in higher losses due to the angles and longer ducts, requiring higher fan power per cubic foot of conditioned air delivered. It is also partially self defeating as it increases the static pressure the fans have to work against, which increases both the losses and noise level.
Thus, it would be desirable, and it is the object of the present invention, to provide a new and improved air conditioning system for buses which achieves the desired passenger comfort during both heating and cooling cycles, without the disadvantages pointed out above.